Year	Percent
1970	29.70279
1971	28.60148
1972	26.60082
1973	27.63647
1974	30.34011
1975	26.67364
1976	27.01751
1977	26.67568
1978	26.46241
1979	25.99793
1980	26.59639
1981	22.60809
1982	21.63237
1983	18.78825
1984	19.84908
1985	19.00676
1986	18.59445
1987	19.66521
1988	21.89496
1989	23.56244
1990	24.38422
1991	22.87578
1992	22.62765
1993	21.96598
1994	22.04699
1995	21.82465
1996	21.67064
1997	22.2953
1998	22.41647
1999	22.71269
2000	23.78182
2001	22.59211
2002	20.6646
2003	20.86068
2004	22.4948
2005	23.60926
2006	23.88416
2007	24.44745
2008	25.73046
2009	21.66442
2010	22.69205
2011	23.99011
2012	23.20454
2013	22.17343
2014	23.31532
2015	23.57776
2016	23.95159
2017	24.62559